The present disclosure relates to exhaust gas purification catalysts and methods for producing the catalysts.
Exhaust gas purification catalysts (three-way catalysts) loading catalytic metals, such as Pt, Pd, or Rh, on oxide supports have been used in order to purify hazardous substances, such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx), emitted from automobile engines.
The exhaust gas purification catalysts include, for example, a catalyst loading Pt on CeO2. This catalyst is known to have a large oxygen storage/release capacity and show excellent performance in oxidizing and purifying CO and HC. The catalyst can efficiently generate H2 through a water gas shift reaction and, thus, promote reduction purification of NOx by using H2 generated.
An exhaust gas purification catalyst becomes active at a predetermined temperature, and can purify the hazardous substances described above in exhaust gas into a nontoxic gas through oxidization or reduction. However, in an initial period of starting up an engine in which the engine is not warmed up enough yet, the temperature of the exhaust gas is low, and thus, the catalyst does not become active. Accordingly, in this initial period, hazardous substances in the exhaust gas are emitted to the air without being purified. To prevent such emission, catalysts that become active at low temperatures, i.e., exhibit excellent exhaust gas purification performance, have been in demand.
Japanese Unexamined Patent Publication No. 2003-265958 describes a catalytic material which is loaded with a precious metal as a catalytic metal on a composite oxide containing CeO2 and ZrO2 as main components and on which a heat treatment has been performed at 600° C. to 1000° C. in a reduction atmosphere. In the catalytic material of Japanese Unexamined Patent Publication No. 2003-265958, a precious metal performs storage/release of lattice oxygen of CeO2, oxygen can be released in a reduction atmosphere even at low temperatures, and thus, the catalytic material can exhibit excellent purification performance of exhaust gas.